To answer this question, the user needs to understand the concept of unit testing and the purpose of each testing technique.

Unit testing is a software testing technique that focuses on individual units or components of a software system. The goal of unit testing is to ensure that each component of the software system performs as expected. During unit testing, various techniques are employed to test the individual units of a software system.

Now, let's go through each option and determine whether it could be done during unit testing or not:

A. Desk check: This is a technique where a developer or tester reviews the code or a document to ensure that it meets the expected quality standards. Desk checking can be performed during unit testing to ensure that the code meets the expected quality standards.

B. Manual support testing: This is a type of testing where a tester manually tests a system to ensure that it meets the expected quality standards. Manual support testing is not performed during unit testing. Instead, it is typically performed during system testing or acceptance testing.

C. Walkthrough: This is a type of software review where a group of people gets together to review the code or a document to ensure that it meets the expected quality standards. Walkthroughs can be performed during unit testing to ensure that the code meets the expected quality standards.

D. Compiler-based testing: This is a type of testing where a compiler is used to check the syntax and semantics of the code. Compiler-based testing can be performed during unit testing to ensure that the code meets the expected quality standards.

Therefore, the correct answer is:

The Answer is: B